Spreading and infiltration of inkjet-printed polymer solution droplets on a porous substrate

Simultaneous spreading and infiltration of inkjet-printed droplets has been studied. Small (54- and 63-microm diameter) droplets of an aqueous polymer solution (2.4 vol% polyacrylic acid, PAA, MW 60,000) were deposited on high green density porous ceramic beds, and the wetting-induced spreading and infiltration of the droplets were characterized. The time scales for spreading and infiltration were comparable (approximately milliseconds), resulting in interruption of the spreading prior to completion by infiltration of the liquid into the powder bed, a situation that has received little treatment in the literature. The infiltration time was varied by changing the pore size (via particle size) in the powder bed, and it was confirmed that slower infiltration resulted in greater spreading of the liquid. The spreading and infiltration of the droplet were modeled to examine the coupling between the two processes and allow prediction of the maximum extension of the droplet as a function of the powder bed particle size. The liquid spreading was found to follow r(t)=a(b+t)(n) behavior, and the effect of particle size on infiltration time was used to predict the point at which spreading ceases due to infiltration for various particle sizes.